This invention relates to improvements in the suspension system for a vehicle, and is specifically related to controlling the disposition of the vehicle body relative to the vehicle wheels when the vehicle is subject to load distribution changes.
In recent times there has been a trend towards resilient sprung suspension systems incorporating variable damping and spring rates in an attempt to improve vehicle stability and reduce generally vertical movement of the vehicle body relative to the surface being traversed. Some more advanced suspension systems, commonly referred to as "active" and "semi-active" suspensions, incorporate a number of electronic sensors which monitor information, such as vertical wheel travel and body roll, as well as speed, acceleration, steering and braking commands. This and other data is processed by a computer which instructs hydraulic or pneumatic actuators to override the normal function of resilient springs in order to interpret, compensate and adjust the suspensions performance to suit speed, terrain and other factors in order to maintain a level ride and controlled distribution of weight to all wheels. These suspension systems require an external intelligent back-up system, and call for a substantial input of external energy, drawn from the vehicle engine, to operate actuators that affect the adjustment to the suspension system.
A range of constructions of "active" and "semi-active" suspensions for vehicles have been proposed including systems operating on the basis of compression and/or displacement of fluids, such systems currently in use incorporate a pump to maintain the working fluid at the required pressure and to effect high speed fluid distribution, and sophisticated control systems to regulate the operation of the suspension system in accordance with sensed road and/or vehicle operating conditions. These known systems incorporating pumps and electronic control systems, that are both required to operate substantially continuous while the vehicle is in operation, and are comparatively expensive to construct and maintain, and require substantial energy input in operation. As a result, these systems have limited acceptability in the vehicle industry.
There is disclosed in International Patent Application No. WO93/01948 a vehicle having a load support body, and a pair of front ground engaging wheels and a pair of rear ground engaging wheels connected to the body to support same, and wherein each wheel is displaceable relative to the body in a generally vertical direction. Interconnected between each wheel and the body is a fluid ram including upper and lower fluid filled chambers that vary in volume in response to vertical movement between the respective wheels and the body. In that suspension system a front wheel ram and the diagonally opposite rear wheel ram have the upper chamber of the front ram interconnected with the lower chamber of the rear ram and the lower chamber of the front ram interconnected to the upper chamber of the rear ram. Similarly the respective chambers of the other front ram and rear ram are likewise interconnected. There is thus provided two individual fluid circuits, each comprising a front ram and a diagonally opposite rear ram. Each of the conduits interconnecting the respective upper and lower chambers has a conventional pressure accumulator in communication therewith. The two circuits are interconnected to a pressure balance device arranged to maintain equip-pressure in the two circuits as is described in detail in the previously referred to International Patent Application No. WO93/01948.
As most vehicles are non-symmetrically loaded for a large portion of the operating time thereof such that loads carried are located so the rear wheels carry more weight than the front wheels, or the load is closer to one side of the vehicle than the other, thus causing the vehicle body to tilt toward the heavier side or end.